The present invention is based on the phenomenon of dielectrophoresis--the translational motion of neutral matter caused by polarization effects in a non-uniform electric field. The dielectrophoresis phenomenon was first recorded over 2500 years ago when it was discovered that rubbed amber attracts bits of fluff and other matter. Over 300 years ago, it was observed that water droplets change shape as they approach a charged piece of amber. The basic concept of dielectrophoresis is examined in detail in a text entitled Dielectrophoresis by Herbert H. Pohl, published in 1978 by the Cambridge University Press. Further discussion of this phenomenon also can be found in an article by W. F. Pickard entitled "Electrical Force Effects in Dielectric Liquids," Progress in Dielectrics 6 (1965)--J. B. Birks and J. Hart, Editors.
All known practical applications of the dielectrophoresis phenomenon have been directed to either separators or clutches. For example, U.S. Pat. No. 1,533,711 discloses a dielectrophoretic device that removes water from oil; U.S. Pat. No. 2,086,666 discloses a dielectrophoretic device which removes wax from oil; U.S. Pat. No. 2,665,246 discloses a dielectrophoretic separator used in a sludge treatment process; U.S. Pat. No. 2,914,453 provides for separation of solid polymeric material from fluid solvents; U.S. Pat. No. 3,162,592 provides for separation of biological cells; U.S. Pat. No. 3,197,393 discloses a separator using centripetal acceleration and the dielectrophoretic phenomenon; U.S. Pat. No. 3,304,251 discloses dielectrophoretic separation of wax from oil; U.S. Pat. No. 3,431,441 provides a dielectrophoretic separator which removes polarizable molecules from plasma; U.S. Pat. No. 3,980,541 discloses separation of water from fluid; and U.S. Pat. No. 4,164,460 provides for removal of particles from a liquid. U.S. Pat. Nos. 3,687,834; 3,795,605; 3,966,575; and 4,057,482 disclose other dielectrophoretic separators for removing particulates and water from a fluid. Other separators, not necessarily dielectrophoretic separators, are disclosed in U.S. Pat. Nos. 465,822; 895,729; 3,247,091 and 4,001,102.
U.S. Pat. No. 2,417,850 discloses a clutch mechanism using the dielectrophoretic phenomenon.
The object of the present invention is to provide a method and apparatus for selectively displaying visual information using the dielectrophoretic effect. A variety of electronic display devices are well known in the art. None of these, however, offer the possible combination of high contrast, high resolution, simple interfacing, and low cost which could be achieved with a dielectrophoretic display in accordance with the present invention. The premier display today is the CRT (cathode ray tube), which provides good resolution, color, and high speed, but which suffers from the effects of ambient light, bulk, complex interfacing, and expense. LED (light emitting diode) display arrays have high speed and are simple to multiplex, but they are inefficient, and they too suffer from ambient light and expense. LCD's (liquid crystal displays) have low power consumption and low cost, but they suffer from poorer contrast, grey scale, speed, and resolution. Other techniques, such as plasma panels, neon discharge tubes, and others, have similarly proved themselves somewhat deficient in at least one of these criteria for an electronic display: efficiency, reliability, contrast, speed, resolution, insensitivity to ambient light, ease of interfacing, and cost. The present invention employs a technique which is new to electronic displays. The effect used to manipulate the display is dielectrophoresis, or the force exerted on electrically neutral matter by non-uniform electric fields.